1. Field of the Invention
This invention relates generally to an apparatus for treatment of wastewater and, more particularly, to an apparatus for aerobic treatment of wastewater in a single tank employing an inverted cone clarifier.
2. Prior Art
Relatively small, self-contained wastewater treatment systems are being employed throughout the country for i treatment of wastewater from domestic sources, particularly single family dwellings located in areas which are not served by a larger municipal collection and treatment system. Strict federal and state clean water standards have resulted in a proliferation of various units designed to produce an effluent which meets those standards. Most states require stringent testing of treatment systems proposed for sale. A relatively small number of small volume aerobic treatment systems have been approved for sale due to the inability of many units to meet the required effluent standards. By far the most popular and accepted test standard is, NSF Standard 40 for Individual Aerobic Wastewater Treatment Plants (revised in June of 1990), known as "NSF Standard 40", as developed by the NSF Joint Committee on Wastewater Technology.
One popular treatment system design employs a single cylindrical tank having an inverted cone clarifier positioned within the tank with four radially spaced air pipes delivering air into the tank outside of the clarifier, as illustrated in U.S. Pat. No. 4,650,577, invented by Mr. Bradley L. Hansel (hereafter referred to as the "inverted cone system"). The geometry of the inverted cone system has proven to be a cost effective and efficient way to treat domestic sewage. However, even these units and variations on the inverted cone system have had some difficulty meeting NSF Standard 40.
Prior art treatment units similar to the inverted cone system have attempted to improve performance by raising the dissolved oxygen content of the wastewater within the tank, thus providing additional support for the aerobic bacteria which feed on the waste. An example of such an attempt can be seen in U.S. Pat. No. 5,221,470, invented by Mr. Jerry L. McKinney. In this system, two air pipes deliver air to the lower portion of the tank and terminate at diffusers, which produce fine bubbles to maximize oxygen transfer to the wastewater. Such systems concentrate on oxygen transfer as opposed to mixing, leaving quiescent zones between air outlet pipes. However, an additional filter was required to attain proper treatment.
Systems can suffer from a loss in treatment efficiency if one or more of the aeration tubes is not functioning. If the bottoms, of the aeration tubes are not level one or more of the tubes may not aerate at the desired rate or may not aerate at all. A unit can be unlevel due to improper installation or a unit may be properly installed initially and then get out of level due to settling of soil or other factors. Aeration tubes can also stop, aerating because of clogging of the openings with particles or bacteria.
What is needed is an improved inverted cone system which will maintain the basic size of the system while increasing treatment efficiency. What is also desired is a unit which can continue to treat efficiently even though is out of level and which will be resistant to clogging of the aeration tubes.